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9/19/2017 7:27:10 PM
Posted: 12/14/2005 10:58:10 AM EDT

I did a test today with my 16" 1/9 twist barrel with 75gr and 68gr rounds.

Hornady Tap 75gr
Black Hills 75gr OTM
Black Hills 68gr OTM

Due to the weather (32 degrees) plus 15-20mph wind and spitting sleet with a little snow mixed in. I was only able to get in 10rds of each at 100yds before calling it quits. I had no keyholes or unusual flyers of any kind. My groups were good considering the weather and the use of iron sights. 3" to 4" prone position. The Black Hills 75gr was the best out of the group for me.

Now that I have given all the background info, here is my question. Would you consider this a good enough test to go and buy a few hundred rounds. Fulton Armory has a good sale on Black Hills and I don't want to miss out.



Link Posted: 12/14/2005 11:12:30 AM EDT
BH 75's out of my 20' 1x9 EGW match barrel, at 100 yards are sub .5 inch! And i am wondering the same thing. I have'nt shot them in cold weather though. I don't know if i should assume they will be stable at longer ranges?
Link Posted: 12/14/2005 12:46:02 PM EDT
Black Hills Blue box is the only ammo the military, Army, Marines, etc.. marksmanship program uses.
Link Posted: 12/14/2005 1:06:51 PM EDT

Originally Posted By Ratgravy:
I haven't shot them in cold weather though. I don't know if i should assume they will be stable at longer ranges?



Don't assume anything. Per BigBore, what is true at 100m may not be true at all at 300m or more.
Link Posted: 12/14/2005 1:07:34 PM EDT

Originally Posted By scar18u2:
Black Hills Blue box is the only ammo the military, Army, Marines, etc.. marksmanship program uses.



Are you affiliated with those programs? I thought they used white box Mk 262 Mod 1 in quantity too.
Link Posted: 12/14/2005 1:47:45 PM EDT
I did a comparison out at 300 yards with my Savage 12 BVSS-S bolt rifle (1 in 9, 26" barrel) and my Colt Hbar Elite (1 in 9, 24" barrel). Didn't notice any significant differnce in accuracy between the 77 gr and 69 gr Sierra matchking bullets. (Both loads were black hills blue box.) If anything the 77 gr stuff shot a tiny bit better at the onger ranges but this may be because it was a little gusty. I've shot the 75 gr stuff out as far as 400 yards without noticing any odd issues like keyholing. For me it kinda answers the question about whether the 1 in 9 rate of twist will stabilize the 75 and 77 gr bullets but I'd like to try a good 1 in 8 barrel to see if I get the same results again. Perhaps the 75 or 77 gr. bullets will shoot even more accurately with a little more spin?
Link Posted: 12/14/2005 3:04:22 PM EDT
[Last Edit: 12/14/2005 3:05:49 PM EDT by blackeye]

Originally Posted By Combat_Jack:

Don't assume anything. Per BigBore, what is true at 100m may not be true at all at 300m or more.



So I take it from your post that someone has had rounds that have been OK at 100yds then destabilize further down range?

The range I was shooting at goes to 300yds. It was just too damn cold, windy and sleet/snowy to stick around very long. Its hard to get good groups with your teeth chattering.

Link Posted: 12/14/2005 4:07:22 PM EDT
I tried Black Hills 77 grain (Sierra Matchkings) and PMC and Black Hills 69 grain (also Sierra Matchkings) from my 16", 1/9 twist, chrome-lined barrel. Excellent groups at 100 yards for both. I shot some 3/4 inch groups with the 77 grain. The 69 grain stuff stayed tight at 200 and 300 yards, but at 200 yards the 77 grain stuff was spread out all over the place and by 300 yards wasn't even on the paper.
Link Posted: 12/14/2005 4:11:10 PM EDT

Originally Posted By blackeye:

Originally Posted By Combat_Jack:

Don't assume anything. Per BigBore, what is true at 100m may not be true at all at 300m or more.



So I take it from your post that someone has had rounds that have been OK at 100yds then destabilize further down range?

The range I was shooting at goes to 300yds. It was just too damn cold, windy and sleet/snowy to stick around very long. Its hard to get good groups with your teeth chattering.




They werent destabilizing farther out, but older, more used barrels may shoot 1 MOA at 100 yards and 4 MOA at 600. No one really has conducted a proper test to see what twist really is needed to stabilize a 75gr bullet.
Link Posted: 12/15/2005 6:44:05 AM EDT
When I was at Camp Perry last summer, the military were definitely shooting Black Hills blue box. I use it in competition as well, the 77Gr Moly Coated version for 200 and 300 yard ranges. I roll my own for the 600 yard course, using a different, moly-coated bullet.

I am sure that you all know the twist rate is dictated not by the weight of the bullet but by its length; long skinny bullets require a higher twist rate than shorter fat ones. Furthermore, the long skinny bullets have a better BC than the short fat ones. Compare the BC for a 40 grain Nosler bullet to the BC of the 75 Gr Hornady AMAX. Of course, heavier bullets are usually longer than lighter bullets so using weight as the indicator for twist rate usually works well.

However, that is not always the case. Compare the 75 gr AMAX to the 77 gr SMK. You will immediately see the AMAX is longer and with a sharper ogive than the SMK, even though it weighs less. So, while your rifle may shoot the 77 gr SMK properly, it may not be able to stabilize the 75 AMAX.

Further, in order to be stable, a bullet needs to retain a certain velocity and rotational speed. For instance, my 75 AMAX loads reach 600 yards in .84 seconds out of my 1:8 twist 20 inch barrel. It leaves the muzzle at 248,400 RPM and 2760FPS (according to my chronograph.) There is a certain threshold in rotation that has to be reached for the bullet to be stabilized. For this one, I believe the figure is 175,000 RPM.

I will not bore you with a discussion on coeeficient of drag and spin decay, but suffice it to say that the rotation and velocity decrease rapidly and at long ranges if your bullet is not supersonic and ois no longer spinning quickly, it may become "erratic". This will be more marked in shorter barrel as the MV is less than the one from longer barrels.

Further more, the air density increases when it is cold, (we all know that airplanes toke off quicker when it's cold outside,) and so the drag on the bullet increases. This is exacerbated by the fact the powder in the bullet might be affected by the temperature and you actually experience quite a drop in muzzle velocity with the corresponding loss of stability downrange.

All this is to say that you should shoot more. :-)

P.S. If you are in any way interested in long range accuracy, get 20 inches of barrel or more and get a 1:8 or faster twist rate. You can then play with the longer (heavier) bullets knowing your rifle can handle them.

If, on the other hand, you are only interested in shooting hordes of zombies coming for your iPod, then I suspect you are fine with your 1:16 or smaller barrel.

The above does not, of course, apply to the military and LE contingent among us.
Link Posted: 12/15/2005 7:54:11 AM EDT

Originally Posted By blackeye:
Now that I have given all the background info, here is my question. Would you consider this a good enough test to go and buy a few hundred rounds. Fulton Armory has a good sale on Black Hills and I don't want to miss out.



Yes,
Link Posted: 12/15/2005 8:33:34 AM EDT
I wanted to add a few more things to my prior post. The following is some chronograph numbers I recorded earlier this year.

This is from my Chrony F1-Master at 12 feet from the muzzle. The first set of loads is Black Hills 77 SMK MC blue box (BS: .362). I show the difference between the barrel lengths. The strings are 10 shots. The temperature was 90 degrees.

In my 20 inch upper (1:8):
Avg Muzzle Velocity: 2522
Standard Deviation: 34
Extreme Spread: 85

In my 24 inch upper (1:8):
Avg MV: 2733
SD: 14
ES: 44

As you can see, the 24 inch barrel gains 210+ FPS and has a smaller SD and ES. The extreme spread is the difference between the lowest and the highest velocity in the string.

The following is my 600 yard load with the Hornady 75 grain AMAX MC. The BC of that bullet is .435 and it does NOT fit in a magazine; it must be loaded one at a time.

In the 20 inch barrel:
Avg MV: 2760
SD: 23
ES: 60

I get another 200FPS in the 24 inch barrel, yes almost 3000FPS for a 75gr bullet with a very high BC.


Please note the use of Moly-Coated bullets.

Link Posted: 12/15/2005 9:14:56 AM EDT
[Last Edit: 12/15/2005 10:10:49 AM EDT by Christian_Gun_Nut]
I had some of the same questions about stability of heavier bullets with a 1:9 twist barrel. I tried my 1:9 twist 16" bushy out to 400 yards so far with no signs of destabilization with BH 75grOTM. In fact, it shoots the best groups, particularly on windy days.

I have friends who have had the 75gr go unstable from their 1:9 twist barrel at 300 yards (actually somewhere between 200 and 300, but we don't know at what range exactly).

Is the test adequate to tell you if you will stabilize 75gr bullets out to 200 and beyond? No. What it does tell you is that 75gr would probably perform well in your weapon for CQB/self defense.

Darn, you have to go to the range again!

Would I buy the ammo from fulton armory if I were you. Heck yes! I just bought a case myself. If you find it doesn't stabilize out to 300 yards, so what. What are the odds of needing defensive ammo past 200 yards around the house? Until you know how your weapon performs with this ammo, I would still have a good amount of your usual ammo around so you have confidence in your weapon in a SHTF situation.
Link Posted: 12/15/2005 12:18:34 PM EDT
The Black Hills 75Gr OTM is NOT the same bullet I was describing for my 600 yard load. The one in the Black Hills ammo seems to be the Hornady 75 Gr HPBT with a BC of .395. The Hornady 75 gr AMAx is a longer bullet with a BC of .435.

The 77gr bullet used in the Black Hills ammo is a Sierra MatchKing, as we already all knew, with a BC of .362.

Indeed, I would go so far as to say the Hornady 75gr OTM (BTHP) is the equivalent of the Sierra MatchKing 77gr; the Sierra MatchKing 80 gr HPBT (BC: .420) is the equivalent of the Hornady 75 gr AMAX. These last two do require a 1:8 or faster twist and will not fit in a standard magazine. The first two will/should work fine in a 1:9 twist and fit in the magazine.

As I said earlier, it's really about length, not weight.
Link Posted: 12/15/2005 12:53:12 PM EDT
Sig685 is obviously correct. While weight and length are correlated, they are not directly related due to differences in bullet design. This is probably why the BH 75gr OTM stabilizes well in so many 1:9 twist barrels. I asked a similar question earlier. You can check out that thread if you like.
http://www.ar15.com/forums/topic.html?b=3&f=16&t=259812
Link Posted: 12/15/2005 1:10:35 PM EDT
[Last Edit: 12/15/2005 2:29:34 PM EDT by Sig685]
I wanted to add that the AMAX is not terribly longer than the 75GR HPBT or the 77GRSMK, but the major difference is in the ogive. The AMAX is so much straighter than the others, it's bearing surface is a lot shorter which is another reason it has to be loaded so far out. A very interesting design. I am also using it in .308. I like the design very much, so I'll stick with it until something better comes along or I develop a problem with it.

Edited to add:

I just read the rules for this forum and I apologize for bringing up reloading information. My bad. I will be at the reloading forum for this stuff. Sorry everyone.
Link Posted: 12/15/2005 5:50:30 PM EDT
The 77/ 75 grain bullets are stable and accurate in all 5 of the 1-9 twist barrels I have fired them through. This has included 16" thru 26" barrels and ranges out to 600 yards. As an aside, a few years ago my wife was quite happy to have fired a 192-5x/200 at Camp Perry at 600 yards with her Bushmaster 1-9 twist, chrome lined, 20" barreled service rifle. At the end of the day we realized she had mistakenly fired 80gr Sierra's that day, instaed of her 75 grain Hornadys. I don't worry about 75/77 grain bullets in a 1-9 twist anymore. They work fine.
Link Posted: 12/16/2005 7:15:24 AM EDT
There is a difference between accuracy and stability. Some bullets won't stabilize, some stabilize but don't group well, and are just plain accurate at any range. Just for shits and giggles I shot some of the remanufactured 75gr Hornady match ammo out of my 1\9 RRA 16" upper. I only tested it at 100 yards but it was plenty accurate. The real question is how accurate would it be at longer ranges? Wolf groups just about as well at 100 yards as any other commercial non match ammo I've used, but the groups open up to be 50% larger at 200 yards than other similar ammo. Match grade ammo will in all probability hold it's group as the range increases because of it's more consistant manufacturing.
Link Posted: 12/16/2005 10:01:15 PM EDT

Originally Posted By Sig685:
I wanted to add a few more things to my prior post. The following is some chronograph numbers I recorded earlier this year. (snip)
As you can see, the 24 inch barrel gains 210+ FPS and has a smaller SD and ES. The extreme spread is the difference between the lowest and the highest velocity in the string.



I'm surprised that an extra four inches of barrel makes such a difference. In the British SA80 weapons, the extra five inches from the L85 to the L86 (20 to 25 inches) is only supposed to add 100 fps.

Tony Williams: Military gun and ammunition website and discussion forum
Link Posted: 12/17/2005 6:41:17 AM EDT
[Last Edit: 12/17/2005 6:42:32 AM EDT by elokoman]
Does anyone know how these will do in shorter barrels such as M-4 or even the pistol length 1/9 barrels?
Link Posted: 12/19/2005 1:37:42 PM EDT
75 gr ammo worked fine out of my 16" barrel so there isnoreason why it wouldn't work out of the 14.5" M4 profile. A pistol length AR is another story altogether.


Originally Posted By elokoman:
Does anyone know how these will do in shorter barrels such as M-4 or even the pistol length 1/9 barrels?

Link Posted: 12/19/2005 1:52:43 PM EDT

Originally Posted By TonyWilliams:

Originally Posted By Sig685:
I wanted to add a few more things to my prior post. The following is some chronograph numbers I recorded earlier this year. (snip)
As you can see, the 24 inch barrel gains 210+ FPS and has a smaller SD and ES. The extreme spread is the difference between the lowest and the highest velocity in the string.



I'm surprised that an extra four inches of barrel makes such a difference. In the British SA80 weapons, the extra five inches from the L85 to the L86 (20 to 25 inches) is only supposed to add 100 fps.

Tony Williams: Military gun and ammunition website and discussion forum



Must be the powder he is using. Most sources predict about a 125 fps gain from 20 to 26 inches.
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